1. Field of the Invention
The present invention relates to a grinder, and more particularly to a hand held grinder.
2. Description of Related Art
With reference to FIG. 9, a conventional hand held grinder in accordance with the prior art comprises a connecting block (90), a bushing (84) and a motor (81) all received in a housing (80). A hollow shank (91) extends from one end of the connecting block (90) and has a threaded exterior surface. A grinding bit (97) is received in the shank (91) after penetrating the housing (80). A chuck (96) is screwed on the shank (91) to hold the grinding bit (97) in place. Two conical holes (92) are defined in opposite sides of the connecting block (90). These two conical holes (92) communicate with each other and receive a steel ball (94) at the junction between the holes (92). A threaded rod (93) is screwed through opposite sides of the housing (80). The facing ends of the threaded rods (93) are concave so that when the ends of the threaded rods (93) abut the steel ball (94) they will hold the steel ball (94) in place. A protrusion (95) extends from the inside end of the connecting block (90). A bearing (85) is mounted on the protrusion (95) and received in the bushing (84). An eccentric shaft (841) extends from the bushing (84) opposite to the bearing (85). A washer (86) is mounted around the eccentric shaft (841). A shaft (82) extend from the motor (81). A coupling (83) is securely mounted on the shaft (82) of the motor (81). A recess (not numbered) is defined in the coupling (83) opposite to the motor (81) to receive the washer (86).
The coupling (83) is driven by the motor (81) that drives the bushing (84) and makes the bushing (84) revolve eccentrically by means of the eccentric shaft (841). The grinding bit (97) is driven by the connecting block (90) and traces ellipses because the protrusion (95) of the connecting block (90) is mounted in the bearing (85) and the bearing (85) is received in the bushing (84).
Even though the conventional hand held grinder can grind the surface of a part precisely, it has several disadvantages.
1. The steel ball (94) and the threaded rod (93) are metal. They are easily worn out and noisy during operating.
2. The bushing (84) directly drives the connecting block (90) without any limitation. It will cause a significant vibration and make user's hand holding the grinder lose feeling.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional hand held grinder.